Although films of polyethylene terephthalate and cellulose acetate have been in wide commercial use as base flexible materials for magnetic recording media, e.g., magnetic audio and video recording tape, recently a number of deficiencies for these films have been recognized. Such deficiencies apply to many practical requirements, such as increase of recording capacity or time for a given volume of recording tape cassette, and improvement of the operation performance thereof. Magnetic recording tapes supported on polyester type film, for example, when it has less than a certain thickness, exhibits poor running performance, such as irregular tape running (so-called stick and slip), clogging on recording heads, appreciable permanent elongation under play-back tension and damage at tape edge. This is because of unsatisfactory mechanical properties of the tape, especially low lengthwise and transverse tensile modulus. Prior art tapes have also other recognized deficiencies, for example, poor dimensional stability both thermally and hygroscopically (causing undesirable sound distortion for audio tape and skew for video tape) and undesirable powder formation upon keeping contact with the recording head and guide pins, causing noise and drop-out. Furthermore, such tapes are not suitable for magnetic duplication by the thermal process using CrO.sub.2 which is the preferable method for better transfer efficiency. This is because of poor dimensional stability of the tape at higher temperatures.
After extensive work to overcome these deficiencies of the prior art, it has now been found that an especially desirable and useful magnetic recording medium can be made from a film or sheet consisting essentially of p-oriented aromatic polycarbonamide units, and that this material has hitherto unattainable highly favorable mechanical and thermal performance characteristics. The medium in accordance with the present invention can provide especially improved magnetic tapes, such as CrO.sub.2 magnetic tapes for thermal duplication, and can produce much thinner tapes with satisfactory stiffness, wear life and excellent runnability compared with conventional magnetic tapes.